1. Field of the Invention
This invention relates to malto-dextrin syrups which remain clear over a relatively long period of time at high solids concentrations. The syrups are particularly useful as extenders for synthetic sweeteners. The invention is also concerned with a method of preparing said syrups wherein the first step includes simultaneous oxidation and liquefaction of the starch at elevated temperatures and conversion with an enzyme.
2. Description of the Prior Art
There are many processes known in the art for producing starch hydrolysates. These processes include liquefying an aqueous slurry of starch with an acid, followed by enzymatic conversion, sometimes referred to as saccharification, or liquefying an aqueous slurry of starch with a liquefying enzyme, followed by enzymatic conversion. For example, Dutch Patent Publication No. 66/12486, published Apr. 3, 1967, discloses a method for hydrolyzing an aqueous slurry of starch with an acid to a D.E. of at least about 7 to no more than about 16, followed by enzymatic conversion with bacterial alpha-amylase to a D.E. in the range of from about 23 to about 35. Products produced by this technique are referred to by the corn wet milling industry as "corn syrup solids" or "glucose solids".
Another known class of starch hydrolysates is referred to by the corn wet milling industry as "malto-dextrins" or "hydrolyzed cereal solids". Malto-dextrins are starch hydrolysates having a measurable dextrose equivalent value not substantially above about 20 and contain a relatively small amount of dextrose and maltose. Generally, the dextrose content of malto-dextrins is less than about 2.4%, by weight and the amount of maltose is less than about 9%, by weight.
Malto-dextrins are commercially available under the tradenames, Mor-Rex, manufactured and sold by Corn Products, a Unit of CPC International Inc., International Plaza, Englewood Cliffs, N.J.; Maltrin, manufactured and sold by Grain Processing Corporation; Frodex, manufactured and sold by American Maize Products Company; and Star-Dri, manufactured and sold by A. E. Staley Manufacturing Company.
Many commercially available malto-dextrins are generally prepared by first liquefying native starch with an acid or an enzyme to a D.E. less than about 15, followed by an enzymatic conversion to the final desired D.E. Products produced by these methods are extremely soluble in water and their concentrated syrups are haze resistant at low temperatures for at least 3 days. One specific method for preparing these unique malto-dextrins is disclosed and claimed in U.S. Pat. No. 3,560,343 and its reissue application Ser. No. 327,335, filed Jan. 29, 1973. This patent and reissue application disclose and claim a process whereby an aqueous slurry of starch is first solubilized with an acid at elevated temperatures to a D.E. less than about 15, followed by enzymatic conversion with a bacterial alpha-amylase enzyme preparation to increase the D.E. by at least 5 to obtain a product having a D.E. of 10 to 25.
U.S. Pat. No. 3,849,194, granted Nov. 19, 1974, discloses and claims a process for preparing waxy starch based malto-dextrins wherein a slurry of waxy starch is liquefied with an enzyme and thereafter converted to the desired D.E. by the action of a bacterial alpha-amylase enzyme preparation. U.S. Pat. No. 3,853,706, granted December 10, 1974, discloses and claims a process for preparing malto-dextrins derived from non-waxy starches by first liquefying and solubilizing non-waxy starch in an aqueous slurry with an enzyme, heating the slurry to a temperature above about 95.degree.. and thereafter converting the heat-treated slurry with a bacterial alpha-amylase enzyme preparation to obtain the desired product. German Patent Publication No. 1,955,392, published June 16, 1971 and British Patent Specification No. 1,274,506, which generally correspond to U.S. Pat. No. 3,663,369 also disclose a process for preparing malto-dextrins, wherein an aqueous slurry of starch is liquefied with an acid or enzyme to a D.E. not substantially above about 3, followed by enzymatic conversion with a bacterial alpha-amylase enzyme preparation to obtain a malto-dextrin having a D.E. not substantially above about 18.
The aforementioned prior art methods provide malto-dextrin products which perform well in many applications, particularly when used as a carrier for synthetic sweeteners. Other applications for the malto-dextrins include use as a bulking or dispersing agent in synthetic creams or coffee whiteners, as a moisture-holding agent in breads, pastries, meats and as a bodying and smoothing agent in puddings, soups, and frozen ice desserts.
The malto-dextrins of the aforementioned prior art methods are first prepared in syrup form and generally dried to a solid. However, many users of malto-dextrins desire a liquid product to reduce handling costs and to eliminate the need for redispersing a dried product. It has been found that one cannot store and/or ship malto-dextrins of the desired low D.E. in highly concentrated form. To date, there is no known economical method for preparing a malto-dextrin syrup at high solids which is resistant to the formation of haze on storage. The malto-dextrins prepared by the aforementioned prior art methods tend to haze when their syrups are in concentrated form, due to the reassociation of the partially degraded starch molecules in the solution. For example, malto-dextrins from corn starch having a D.E. less than about 20 when concentrated up to about 70% solids tend to quickly haze upon storage, until the point where the product sets up to a solid. Attempts to produce a waxy malto-dextrin product at about a 70% solids content or above and having a D.E. less than about 15, results in hazing when the syrup is stored for long periods of time, i.e., more than about three days.
It has been disclosed in U.S. Pat. Nos. 3,616,219 and 3,709,788, that bleached starches can be treated with bacterial alpha-amylase enzyme preparations. These products are useful as adhesives and coatings in the manufacture of paper and textile products.
Bleached starches are starches produced by an oxidative treatment which leads to a marked whitening of the starch. Generally, the severity of the oxidative treatment is controlled so that the carotene, xanthophyll and related pigments naturally occurring in the starch are efficiently oxidized to colorless compounds while the starch product is only slightly oxidized (D.S. .ltoreq. 0.1 as later defined) if at all. Bleaching may be carried out either in a dry state or in solution and a wide variety of oxidizing agents may be employed; the only restrictive requirement being that the oxidizer chosen must be mild enough under the chosen reaction conditions so that the starch will not be excessively attacked and the oxidizer must be strong enough so that the pigments will be effectively oxidized. Examples of usable bleaching agents include, but are not limited to, chlorine, bromine, hypochlorite, permanganate, ozone, chlorites and chlorites in combination with persulfates. Methods of bleaching starch are discussed in more detail in "Chemistry and Industry of Starch", second edition, R. W. Kerr, editor, Academic Press, Inc., New York, N.Y. (1950).
Oxidized starches are starches produced from the oxidative treatment of the starch which leads to chemical changes in the starch. For example, oxidation of primary alcohol groups to carboxyl groups, of aldehyde groups to carboxyl groups, of secondary alcohol groups to ketone groups, and of glycol groups to carboxyl groups. The oxidation of starch leads to a starch product which is more easily solubilized and which exhibits a lower viscosity when solubilized in water. Oxidation may be carried out by utilizing any of a number of oxidizing agents. Often the oxidizing agents used to form oxidized starch are the same agents that are used to bleach starch. Harsher reaction conditions such as higher temperatures, longer contact times, different pH, etc., are used to cause these agents to react with the starch molecules rather than just the carotene, etc. Reagents used in the oxidation of starch include, but are not limited to air, bleaching powder, halogens, chloramines, chloric acid, chlorates, chromic acid, ferric-chloride, hydrogen peroxide, hypochlorite, manganese dioxide, nitric acid, nitrogen dioxide, perborates, periodic acid, persulfates, potassium dioxide, potassium permanganate, silver oxide, p-toluene sulfochloramide and zinc oxide. Methods of oxidizing starch are also disclosed in more detail in the previously cited text, "Chemistry and Industry of Starch".
The repeating anhydroglucose units in starch may have different degrees of substitution (D.S.), i.e., from one to three, and starch derivatives are generally categorized in terms of their D.S. In a given quantity of a starch derivative, there will generally be some anhydroglucose units that are not substituted at all (i.e., D.S.,O), together with other anhydroglucose units that have different degrees of substitution, from 1 to 3. A statistical average is employed to characterize the average D.S. of the entire quantity, although the figure is ordinarily stated as the D.S. rather than the average D.S. The oxidized starch treated according to this invention may have a varying range of D.S. (carboxyl substitution) which may be as little as 0.0001, up to the maximum level of 3.0. Irrespective of the number of molecules of starch which are reacted, or the actual sequence of substitution, or the number of anhydroglucose units involved, the general formula is intended to represent products where the substitution may occur to various degrees of substitution at all or less than all anhydroglucose units in all or less than all starch molecules.
The distinction between oxidized and bleached starches is now well known to those skilled in the art, particularly the corn wet milling industry. Such a distinction is described in U.S. Pat. No. 3,598,622, the disclosure of which is incorporated herein by reference.
In view of the difficulty incurred by the prior art in producing haze-free starch hydrolysates from untreated starch and the inability to provide haze-free, malto-dextrins from bleached starches, the art has not attempted to produce malto-dextrins from oxidized starch.